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Old   May 20, 2004, 08:10
Default UDF wall velocity
  #1
Avesta
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hello is it possible to define velocity of fluid near wall(slip flow):U=B*(dU/dx or dy)^n and write udf for this boundary condition? if n=0.9 & B=0.02, is this udf is correct?

#include "udf.h"

DEFINE_PROFILE(slip, c, t) {

cell_t c;

Thread *t; double m =C_DWDX(c, t);

C_W(c, t)=0.02* pow ( m, 0.9); }

Yours faithfully Arash Avesta
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Old   May 20, 2004, 10:15
Default Re: UDF wall velocity
  #2
Andrew Garrard
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Your value for slip should be possible to define using a UDF and if you want to define velocity at the wall you can hook it in at the wall boundary condition panel under the moving wall tab. I would use a Define Profile macro, however, you need the arguments (name, t, i). where name is the name that appears in the Fluent GUI, t is the thread (in this case wall that you apply the UDF to) and i is the this you are going to alter(presumably x, y, or z velocity at the wall)

Therefor you will not beed to define t with the Thread *t; line that you have. You will also need a face loop and an F_PROFILE(f, t, i) = line. If you don't understand these terms it is probably best you consult the fluent 6/6.1 UDF manual.
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Old   May 21, 2004, 06:09
Default ?UDF wall velocity
  #3
Avesta
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hello thank you is it possible to define velocity of fluid near wall(slip flow):U=B*(dU/dx or dy)^n and write udf for this boundary condition? if n=0.9 & B=0.02, is this udf is correct?

#include "udf.h"

DEFINE_PROFILE(slip, thread, nw) { cell_t c; Thread *t; int i;

face_t f;

begin_f_loop (f,thread)

double m =C_DWDY(c, t);

{

F_PROFILE(f,thread,nw) = 0.02* pow ( m, 0.9);

} end_f_loop (f,thread) } please if it is not correct,write it for me correctly

Yours faithfully Arash Avesta

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Old   May 21, 2004, 06:51
Default Re: ?UDF wall velocity
  #4
Andrew Garrard
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I haven't used the C_DWDY(c, t) macro befor, so I can't offer you any help with this. However, I know what you do not need to define you thread again with the Thread *t and you don't use variable i, so you wont need this. Your f_loop should be held within {} brackets. Here is what I would do: #include "udf.h"

DEFINE_PROFILE(slip, thread, nw)

{

face_t f;

begin_f_loop (f, thread)

{

cell_t c;

double m =C_DWDY(c, t);

F_PROFILE(f, thread, nw) = 0.02* pow (m, 0.9);

} end_f_loop (f,thread)

}

The last remaining problem with this code is the fact you have not defined c. What cell are you refering to in the C_DWDY(c, t) line. If it is the one next to the boundary face then there are macros for getting this cell avabliable, the information is in the UDF manual.

Happy coding
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